For optical performance, electromagnetic wave transmitters require that the transmitter output stage impedance match the antenna that the transmitter is driving. The impedance match is a function of frequency. Accordingly, a variation in the frequency of the signal being output from the transmitter alters its output impedance, thus requiring the antenna impedance to change, too, to maintain the impedance match.
Traditionally, impedance matching has been accomplished with mechanical tuned inductors and capacitors. However, modern transmitters often change frequency at millisecond time intervals, which precludes mechanical adjustments to inductors and/or capacitors. Thus, with modern transmitters, impedance matching has been accomplished by changing the capacitance of an impedance matching circuit used with the antenna through the use of diodes. The capacitance of a reverse biased diode varies with bias voltage. This phenomenon is exploited by connecting the reversed biased diode to an inductor. Varying the diode bias will change the resonance of the inductor diode circuit. However, the use of diodes limits the dynamic range of tuning. The range that the capacitance of a reversed biased diode that can be varied over is limited and the inductor inductance is fixed, so the range that the resonance can be changed is limited.
Accordingly, it would be desirable to provide an impedance matching system that monitors the frequency of a transmitter and automatically adjusts the impedance of an antenna element being driven by the transmitter, in real time, to maintain the impedance of the antenna element matched with the impedance of the output stage of the transmitter.